Patent Literature 1 discloses a technology of accurately estimating a DPF temperature (i.e., a catalyst bed temperature) even during execution of idle stop in a diesel engine capable of carrying out idle stop to automatically stop the diesel engine during an idling operation. The DPF temperature is estimated in consideration of an amount of heat radiation of a catalyst and an amount of heat transfer thereof by using the temperature of exhaust gas on an upstream side of the catalyst during the execution of idle stop.
Patent Literature 2 also discloses a diesel engine that carries out idle stop to automatically stop the diesel engine during an idling operation. In the diesel engine of this conventional art, when shift to an idling operation is carried out during execution of regeneration of a DPF by post injection of fuel, idle stop is prohibited until the regeneration of the DPF is completed, and the regeneration of the DPF is continued during the idling operation. The reason therefor is that in a case where idle stop is carried out during execution of regeneration of the DPF and regeneration of the DPF is interrupted, a remarkable drop of the temperature of the DPF is caused to thereby necessitate a prolonged time and large energy until regeneration of the DPF is terminated.
However, in the above conventional art in which when shift to the idling operation is carried out during execution of regeneration of the DPF, idle stop is prohibited until the regeneration of the DPF is terminated, opportunity and frequency of conducting the idle stop is necessarily reduced, thereby lowering an effect of reducing exhaust gas and enhancing fuel economy by conducting the idle stop. To solve the above problem, the applicant of the present patent application has considered that when shift to idle stop is carried out during execution of regeneration of the DPF, the regeneration of the DPF is temporarily interrupted, and the regeneration of the DPF is restarted after shift from the idle stop to automatic restart of the engine is carried out.
However, in such a case where the regeneration of the DPF is restarted after carrying out shift from the idle stop to automatic restart of the engine, a difference between an estimation value of the temperature of the DPF and an actual temperature of the DPF tends to occur. Specifically, when fuel supply is stopped and idle stop is carried out, air is supplied into exhaust gas by idling until the engine is stopped, so that an oxygen concentration in the DPF becomes higher. Due to such an event, when post injection of fuel is carried out upon restarting regeneration of the DPF similarly to before interruption of regeneration of the DPF, there occurs an excessive temperature rise in which the temperature of the DPF temporarily becomes excessively higher. The excessive temperature rise tends to cause an adverse influence on the DPF or a drop in fuel economy.